1. Field of the Invention
The invention relates to a method for locating the longitudinal position, either on the front end or on the rear end of a vehicle with an engine, of wheels fitted with an electronic module adapted to send, to a central processing unit mounted on the vehicle, signals representative of operating parameters of each wheel also comprising an identification code of the latter.
2. Description of the Related Art
For safety purposes, motor vehicles are increasingly being fitted with monitoring systems comprising sensors mounted on each of the wheels of the vehicle, dedicated to measuring parameters, such as pressure or temperature of the tires fitted on these wheels, and intended to inform the driver of any abnormal variation of the measured parameter.
These monitoring systems are conventionally provided:                with an electronic module mounted on each of the wheels of the vehicle, incorporating, in addition to the abovementioned sensors, a microprocessor and a radiofrequency sender (or RF sender), and        with a central processing unit, mounted on the vehicle, to receive the signals sent by the senders. This central processing unit comprises a computer incorporating a radiofrequency receiver (or RF receiver) connected to an antenna.        
One of the problems that such monitoring systems have to resolve lies in the obligation to have to associate with each signal received by the receiver of the central processing unit, an indication concerning the location of the electronic module and therefore of the wheel originating this signal, this obligation lasting for the lifetime of the vehicle, that is, having to be observed even after wheel changes or more simply change of the positions of these wheels.
At the present time, a first locating method consists in incorporating an accelerometer in each electronic module, and in implementing a locating technique based on statistical methods consisting in comparing the accelerations of the different wheels to obtain an indication concerning the respective position of each of said wheels.
However, this locating method has proven inefficient because it requires a significant running time in order to produce a discrimination between the different wheels.
A second locating method consists in using three low-frequency antennas, each positioned close to one of the wheels of the vehicle, and in performing a locating procedure consisting in successively exciting each of these three antennas by sending a low-frequency magnetic field.
According to this procedure, the electronic module mounted on the wheel located close to the excited antenna sends, in response and addressed to the central processing unit, a low-frequency signal comprising an identification code of said module, such that the successive excitation of the three antennas results in the locating of the three electronic modules mounted on the wheels close to these antennas, and, by deduction, in the locating of the fourth module.
The main advantage of such a method lies in the fact that the locating procedure is very rapid and leads to an almost instantaneous locating after the vehicle has started up.
However, this solution is very costly because it means fitting the vehicle with three antennas, with all the respective limitations: connecting cables, control amplifiers, etc.